<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        #result {
            width: 200px;
            height: 100px;
            border: 1px solid red;
        }
    </style>
</head>
<body>
    用户名：<input type="text" id="username">
    <p></p>
    <script>
        const input = document.querySelector("input");
        const p = document.querySelector("p");

        // 处理数据
        function handle(data) {
            input.style.border = "1px solid #f00";
            p.innerHTML = data.msg;
        }

        // 绑定事件
        input.onblur = function() {
            // 获取用户输入
            let usr = this.value;
            // 向服务端发送请求
            // 1. 创建script标签
            const script = document.createElement("script");
            // 2. 设置src属性
            script.src = "http://127.0.0.1:8000/check-username";
            // 3. 将script插入到文档中
            document.body.appendChild(script);
        }
    </script>
</body>
</html>